Granular pesticide composition

ABSTRACT

A granular pesticide composition is prepared by reacting polyvinyl alcohol, pesticide, a borate, and optional filler(s) in water until a gel is formed, drying the gel, and then grinding the product to the desired particle size. The product is then applied to the soil for controlling pests.

.Iadd.This is an application for reissue of U.S. Pat. No. 4,440,746granted Apr. 3, 1985. .Iaddend.

BACKGROUND OF THE INVENTION

This invention relates to a composition and method of treating the soilwith a slow release matrix-carried pesticide for controlled, sustainedrelease of active agents contained within the matrix to protect plantsfrom damage by various pests. More particularly, the inventioncomprehends the use of a polyvinyl alcohol (PVA)-borate based releasesystem for pesticides applied to the soil. U.S. Pat. No. 4,110,431discloses the use of polyvinyl alcohol-borate complexes formed by wateractivation of mixtures of the PVA and borax in situ for attaching planttreatment additives to plane foliage. Japanese Patent No. 74/48073describes the use of borax to harden PVA used in the form ofmicro-capsules to encapsulate perfume and flame retardants. SouthAfrican Patent Nos. 69/00122 and 69/00088 teach the use of PVA-boratecapsules for plasticizers and dyes.

SUMMARY OF THE INVENTION

The present invention is directed to a granular, slow releasematrix-carried pesticide prepared by reacting an aqueous solution ofpolyvinyl alcohol and the desired pesticide plus optional filler(s) witha borate with agitation until the reaction is complete forming a gel,drying the gel, and grinding the dried product to the desired particlesize. This produce is then applied to the soil where it slowly releasesthe pesticide for controlling the desired pest.

DETAILED DESCRIPTION OF THE INVENTION

The present invention requires a water soluble polyvinyl alcohol, aborate, and optional filler(s). When the pesticide-containing polyvinylalcohol solution and the borate are combined, they form a didiolcomplex, as indicated below: ##STR1## The reaction mixture thereby gelsand entraps the pesticide in a matrix. The matrix is freed from water bydrying, and then further refined by grinding and screening to thedesired particle size. Granulates in the 14-40 mesh range are preferred.

Any pesticide which is compatible with the matrix can be employed forthe present invention. Typical examples are chlorpyrifos,chlorpyrifos-methyl, methyl parathion, parathion, diazinon, fonofos,fensulfothion, phorate, trifluralin, etc., which can be used undiluted,in the form of suited solutions, on fillers, or in combinations.

As far as polyvinyl alcohol is concerned, any water soluble grade can beused in the practice of this invention. Suited typical commercialproducts are the various partially or fully hydrolyzed polyvinylacetates sold in various molecular weight ranges under the trade namesof Gelvatol, Vinol, Elvanol, etc. Preferred are products which arecharacterized by high solubility/low viscosity in water.

For effecting gelation of PVA, various sources of borate ions can beused. Suited materials are alkali metal, alkaline earth metal andammonium salts of borate anions such as tetraborate and metaborateanions. Examples are sodium borate (borax), sodium metaborate, andpotassium borate. Also combinations of boric acid and alkalizing agentsare effective.

With respect to optional filler(s), a large variety of powdered orgranular materials can be employed in the practice of this invention.Examples are various diatomites, attapulgites, bentonites, talcs,montmorillonites, perlites, vermiculites, calcium carbonates, corn cobgrits, wood flour, lignin sulfonates, etc.

The amounts of the various ingredients in the total formulation can varywidely, and range from about 5-90% (by weight) of PVA, 2-50% of theactive ingredient(s), 0-80% of the filler(s), and 1-20% of borate.Preferred ranges are: 5-70% of PVA, 5-30% of active ingredient(s), and30-80% of filler(s). The amount of borate required to effect gelationvaries with the type and amount of PVA and filler(s) used in theparticular formulation and is best determined experimentally.

EXAMPLE I

Twenty grams of PVA (marketed by the Monsanto Corporation under thetradename Gelvatol 9000) were dissolved in 180 grams of deionized waterto yield 200 grams of a 10% PVA solution. Ten grams of a technical grademethyl parathion (76% active) was dispersed in the 10% PVA solution.Twenty-one grams of a 10% sodium borate (borax) in water solution wasthen added to the PVA-methyl parathion dispersion and reacted withstirring until an opaque gel formed. The PVA-methyl parathion gel wasdried in a forced air oven at 55° C. for 16 hours, yielding 29.7 gramsof product. The dried product was then ground in a blender to a particlesize that would pass through a number 14 mesh screen but remained on anumber 40 mesh screen. This particulate material was found to contain25.1% active ingredient.

EXAMPLE II

Eight grams of Gelvatol 9000 were dissolved in 72 grams deionized wateryielding 80 grams of a 10% PVA solution. Into this 5 grams of Dursban XM(a commercial chlorpyrifos at 65% active ingredient) was dispersed.Three grams of sodium borate (borax) were then dissolved in 15 grams ofwater and added to the PVA-Dursban XM dispersion and reacted until a gelprecipitate formed. This gel precipitate was then dried in an exhausthood for 24 hours to yield 14.2 grams of product. The dried product wasthen ground to a particle size that would pass through a number 14 meshscreen but yet remained on a number 40 mesh screen. The granular productwas found to contain 14.5% active ingredient.

EXAMPLE III

Five grams of Gelvatol 9000 were dissolved in 45 grams deionized water.To this solution 19.0 grams of methyl parathion-loaded Diatomite[prepared by soaking 13.5 grams of Celatom MN-39 (Eagle Pitcher) with4.5 grams technical methyl parathion in ˜40 grams methylene chloride,and removing volatile components at ˜50° C./130 mm Hg] were added,followed by dropwise addition of 5 grams of warm 10% borax solution. Theresulting gel was dried in an exhaust hood for 24 hours, and then in anoven at ˜75° C. for 21/2 hours. The dry product (23.4 grams) was groundin a blender and then classified to yield 14.3 grams product of 14-40mesh size. It contained 13.2% active ingredient.

EXAMPLE IV

The granular product of Example I was tested in a laboratory soilbioassay using 3 day oid housefly larvae as test organisms. Twenty-fivehousefly larvae were exposed to soil at intervals of 3, 10, 17, 38, and45 days following treatment with the granular product and the number ofadult flies emerging from the soil was counted. The granular product wasused at a rate equivalent to 1/2 pound of active ingredient per acreapplied in 6" bands spaced 40" apart.

For the sake of comparison, a commercial formulation of methyl parathionwas also tested at the same level of active ingredient and the resultsof both products were recorded in Table I. % Control is defined as thepercent reduction in adult housefly emergence.

                  TABLE I                                                         ______________________________________                                        % Control                                                                                3      10     17       38   45                                     ______________________________________                                        PVA Matrix   39.0     93.8   91.9   65.3 76.4                                 Methyl Parathion EC                                                                        21.0     10.4   14.9   3.9  0.0                                  Control      0.0      4.0    1.3    10.7 23.4                                 ______________________________________                                    

EXAMPLE V

The granular product of Example II was then tested for bioactivity insoil as in Example IV.

For the sake of comparison, a commercial formulation of chlorpyrifos(Lorsban® 15G) was tested. The results of both products were recorded inTable II as follows:

                  TABLE II                                                        ______________________________________                                        % Control                                                                              3      10     17       24   31                                       ______________________________________                                        PVA Matrix 97.9     98.0   96.9   80.7 75.0                                   Lorsban 15G                                                                              91.4     96.0   96.9   68.6 39.6                                   Control    6.7      0.0    4.0    1.3  6.0                                    ______________________________________                                    

EXAMPLE VI

In the laboratory soil bioassay with 3 day old housefly larvae, theproduct of Example III showed the following activity as compared to themethyl parathion-loaded filler without PVA matrix:

                  TABLE III                                                       ______________________________________                                        % Control                                                                                 3    17         31     45                                         ______________________________________                                        PVA Matrix    84.3   60.9       74.0 72.0                                     MP-loaded Filler                                                                            94.8   57.9       54.0 0                                        Control       4.0    2.7        0    10.7                                     ______________________________________                                    

As evident, the PVA matrix formulation exhibited a much longer-lastinginsecticidal activity than a comparable formulation without the matrix.

What is claimed:
 1. A granular slow release soil pesticide composition.Iadd.comprising by weight based on the total composition of from about5 to about 90% of polyvinyl alcohol, from about 1 to about 20% of aborate, from about 2 to about 50% of a compatible pesticide, and 0 toabout 80% of filler(s) .Iaddend.prepared by mixing .[.from about 5 toabout 90% by weight of.]. (.Iadd.a) .Iaddend.an aqueous solution ofpolyvinyl alcohol .Iadd.wherein the solids concentration of polyvinylalcohol is about 10% .Iaddend.and .[.from about 2 to about 50% of.]. acompatible pesticide .[.plus 0 to about 80% of.]. .Iadd.and optionally.Iaddend.at least one filler selected from the class consisting ofdiatomites, attapulgites, bentonites, talcs, montmorillonites, perlites,vermiculites, calcium carbonates, corn cob grits, wood flour, ligninsulfonates, and mixtures thereof with .[.from about 1 to about 20% of.].(.Iadd.b) .Iaddend.a borate until .[.said.]. ingredients (.Iadd.a) and(b) .Iaddend.react to form a gel, drying the gel, and grinding the driedproduct to the desired particle size.
 2. The composition of claim 1wherein the pesticide is selected from the group consisting ofchlorpyrifos, chlorpyrifos-methyl, diazinon, fonofos, parathion,fensulfothion, methyl parathion, phorate, and trifluralin.
 3. Thecomposition of claim 1 wherein the product is ground to pass through anumber 14 mesh screen but is retained on a number 40 mesh screen.
 4. Amethod of controlling pests comprising applying an effective amount ofthe composition of claim 1 to soil. .Iadd.5. A method of encapsulating apesticide comprising the steps of:a. preparing a solution or dispersionof such pesticide in a matrix-forming material comprising an aqueoussolution of a gel-forming polyvinyl alcohol wherein said aqueoussolution has a solids concentration of said polyvinyl alcohol of about10%, wherein the relative amount of said polyvinyl alcohol with respectto said pesticide is sufficient to entrap said pesticide within a matrixof said polyvinyl alcohol; b. reacting said polyvinyl alcohol with aborate to form a continuous insolubilized matrix gel having entrappedtherein uniformly dispersed, discontinuous domains of said pesticide;and c. recovering free-flowing particles of said entrapped pesticide..Iaddend. .Iadd.6. A composition of matter produced by the process ofclaim
 5. .Iaddend.